Duckweed dying

[Fred]

Hi,

I recently added a small 20 gallon tank to my AP system (55 gallon).  I'm using a small 1/8" line from my main pump to pump water from the AP tank to my duckweed tank.  The Duckweed tank has an overflow near the top that empties back into the AP tank (quite slowly).

I recently added some duckweed and waited for the explosion of growth... and waited.

I've been testing my water regularly and it's in the 7.9 - 8.1 PH range.  ammonia is low (.25) as are nitrites (.25).  Nitrates have remained high in my system since cycling about 80.

The system has been running for about 3 months and has 18 tilapia close to an inch long now.

I've attached some pictures of the duckweed tank just after adding the duckweed and now about a week later.  They appear to be turning white and I see no increase of their volume.

Due to the small input line (pointed down towards the bottom) there is a very small circular motion on top of the water.  The tank is under my AP grow beds but has about 25% exposure to direct sunlight for 1-2 hours during the day while the rest of the day it is shaded.

Is it possible I have a lack of iron in the water?  The plants in my growbed are doing ok (nothing spectacular yet).

Any suggestions?

Before

5 days later (loss of green color)

[Keith Rowan]

i think it needs more light..

[Rick Stillwagon]

http://infohouse.p2ric.org/ref/09/08875.htm      This is the web address of a comprehensive study in duckweed cultivation.

[Ken Elrich]

You might want to consider adding manure (cow, horse, donkey).

I have read where someone uses Donkey manure to increase the nitrogen levels.

I have experienced same issues you have, I have mine in the basement with grow lights.

I have seen better results by using separate tank from the AP system and adding the fish

waste solids to it. the Duckweed lives longer now but no new growth, Probably because of 

improper lighting.   

[RupertofOZ]

The problem of poor duckweed growth.. as posted... is probably the same reason I would NOT add animal manures ... "to increase nitrogen levels"...

(There are other reasons for not adding animal manures to an AP system as well)

 

Duckweed is one of the few plants that actually prefers to grow directly by ammonia... not nitrates (nitrogen)...

 

In the posters example... the duckweed is growing in a tank... at the end of the process... after the ammonia has been nitrified...

 

Hence why Ken sees the results he does...

I have seen better results by using separate tank from the AP system and adding the fish waste solids to it. the Duckweed lives longer now but no new growth, Probably because of improper lighting.

 

The fish wastes are generating the ammonia needed for the duckweed... the poor results as suggested, due to low light...

[Ken Elrich]

thanks RupertofOZ,

I will try making the changes for better results. I want duckweed! I live in Michigan, and with

winter just around the corner I would like the added resource for feeding my tilapia. 

[Bob Terrell]

Couldf you add small amounts of compist tea to the system?   I really don't kniow the answer or the pro's or con's of such an idea.

RupertofOZ said:

The problem of poor duckweed growth.. as posted... is probably the same reason I would NOT add animal manures ... "to increase nitrogen levels"...

(There are other reasons for not adding animal manures to an AP system as well)

 

Duckweed is one of the few plants that actually prefers to grow directly by ammonia... not nitrates (nitrogen)...

 

In the posters example... the duckweed is growing in a tank... at the end of the process... after the ammonia has been nitrified...

 

Hence why Ken sees the results he does...

I have seen better results by using separate tank from the AP system and adding the fish waste solids to it. the Duckweed lives longer now but no new growth, Probably because of improper lighting.

 

The fish wastes are generating the ammonia needed for the duckweed... the poor results as suggested, due to low light...